Apparatus for supplying fluid to a reversible drive organ

ABSTRACT

Fluid supply system for a double acting fluid drive mechanism having first and second drive chambers, the system including a pump whose delivery is connected by a first conduit to the first chamber, a second conduit connecting the second chamber to a reservoir and including a one-way valve permitting flow only to the reservoir, a third conduit coupled to the second conduit, bypassing the one-way valve and including a flow limiter, a fourth conduit connected to the first conduit and to the flow limiter, which latter comprises a discharge valve operable to maintain pressure in the third conduit upstream of the discharge valve and an adjustable valve between the second chamber and the discharge valve operable to control the pressure delivered by the second chamber in response to pressure in the fourth conduit.

United States Patent [191 Martin [45] June 18, 1974 APPARATUS FORSUPPLYING FLUID TO A Primary Examiner-Edgar W. Geoghegan REVERSIBLEDRIVE ORGAN Attorney, Agent, or Firm-Nathaniel A. Humphries, [75]Inventor: Louis E. Martin, Senlis, France [73] Assignee: Societe AnonymePoclain, Oise,

France [57] ABSTRACT [22] Filed: May 22, 7 Fluid supply system for adouble acting fluid drive mechanism having first and second drivechambers, PP 363,168 the system including a pump whose delivery isconnected by a first conduit to the first chamber, a second [30] ForeignApplication p i i Data conduit connecting the second chamber to areservoir M 31 1972 France 72 19573 and including a one-way valvepermitting flow only to ay the reservoir, a third conduit coupled to thesecond conduit, by-passing the one-way valve and including a 5 flowlimiter, a fourth conduit connected to the first [58] d /420, 60/477conduit and to the flow limiter, which latter comprises 1e a dischargevalve operable to maintain pressure in the third conduit upstream of thedischarge valve and an [56] References Cited adjustable valve betweenthe second chamber and the UNITED STATES PATENTS discharge valveoperable to control the pressure delivl,972,462 9/1934 Schafer 91/420 Xgred by the second chamber in response to pressure in 2,328,980 9/1943Herman et al. h f h d i 2,470,778 5/1949 Lankovski et a1. 91/420 X 4Claims, 3 Drawing Figures n -il 20 I n 7 /6 l T 1 APPARATUS FORSUPPLYING FLUID TO A REVERSIBLE DRIVE ORGAN Fluid supply apparatus arealready known which have, arranged in the delivery conduit, aflow-limiter operated by the pressure of the fluid contained in theintake conduit.

However, apparatus of this type have the disadvantage of being ofunstable operation. Moreover, the very operating characteristics areoften mediocre, the opening time of the flow-limiter being badlycontrolled and the closure time being too long.

In order to correct this state of affairs, a flow-limiter of a noveltype is proposed, which has advantages over the previously knownlimiters, without having their above-mentioned disadvantages.

The object of the invention is therefore an apparatus for supplyingfluid to a reversible drive organ, which is connected to a load whichprovides its forced drive during the operating phase in question andwhich has first and second chambers, this supply apparatus consistingof:

a fluid reservoir,

a pump connected to the said reservoir by a suction conduit,

a first conduit, which connects the delivery side of the pump to thefirst of the said chambers, this first chamber forming the fluid intakechamber during the abovementioned operating phase,

a second conduit, which connects the second of the said chambers to thereservoir, this second chamber forming the fluid delivery chamber duringthe said operating phase,

a non-return valve which is arranged in the second conduit and whichonly allows passage of the fluid towards the second chamber,

a third conduit, which is connected to the said second conduit on eitherside of the non-return valve and in which is arranged an adjustable flowlimiter,

a fourth conduit, which is connected on the one hand to the firstconduit and on the other to the flow adjustment organ of the saidflowlimiter.

The adjustable flow limiteritself consists of:

an adjusted discharge valve, which acts to maintain the pressure of thefluid which can be contained in the portion of the third conduit whichis connected to the said discharge valve and is arranged directlydownstream of this valve relative to the reservoir, substantially equalto a given value,

and a valve with adjustable opening, which is arranged between the driveorgan and the discharge valve, which is distinct from this dischargevalve, and the function of which is to regulate the value of thepressure of the fluid which can be delivered out of the second chamberduring the abovementioned operating phase. This valve with adjustableopening includes an organ for adjusting its opening, which is inequilibrium under the antagonistic influences, firstly, of the pressureof the fluid contained in the fourth conduit and, secondly, of the fluidpressure which is substantially equal to the given value.

The valve with adjustable opening is also advantageously provided with ashock-absorber for its opening motion. The said shock-absorber consistsof a piston, which is linked to the organ for adjusting the opening ofthe said valve with adjustable opening, being mounted slidably in thebody of the said valve, and which, with the said body, defines on theone hand a first volume, which is freely in communication with theportion of the third conduit connected to the discharge valve and, onthe other hand, a second volume. A nonretum valve allows passage of thefluid from the first volume towards the second volume, while acalibrated channel, forming a restriction, connects the two saidvolumes. A retaining organ tends "to keep the said piston and the saidadjustment organ linked together.

Preferably, the organ for adjusting the opening of the valve withadjustable opening consists of a slide mounted slidably in the body ofthe said valve. This slide has a shoulder, the lateral adjacent wall ofwhich can overlap the edge of a throat formed in the said valve body,one of the elements the lateral wall of the shoulder or the throatbeingprovided with grooves having progressively vairable sections.

Finally, an elastic return organ :is often inserted between the organfor adjusting the opening of the valve with adjustable opening and thesaid valve body and has an effect antagonistic to that of the pressureof the fluid contained in the fourth conduit.

A better understanding of the invention will be obtained and secondaryfeatures and their advantages will become apparent in the course of thefollowing description of embodiments offered by way of example.

It will be understood that the description and drawings are only givenfor guidance and are not limiting.

Reference will be made to the attached drawings, in which:

FIG. 1 is a diagram of a supply apparatus forming an application for aflow-limiter in accordance with the invention;

FIG. 2 is a sectional view of the adjustable flowlimiter with which thesupply apparatus shown in FIG. 1 is fitted;

FIG. 3 is a section of a modification of a detail of the flow-limitershown in FIG. 2.

In FIG. 1, the presence will be noted of a reversible drive organ which,in this particular case, consists of a double-acting, hydraulic ram l.The piston 2 of this ram defines with body 3 a first chamber 4 and asecond chamber 5. The rod 6 of the piston is arranged substantiallyvertically, while a mass 7 is linked to it by means of a clevis 8 andpin 9, and constitutes a load which tends to return rod 6 into body 3.In this configuration, the first chamber 4 is arranged above the secondchamber 5.

A pump 10 and a fluid reservoir 11 are connected by the suction conduit12 of the pump. In addition, a three-position distributor 13 isconnected, by a first conduit 14, to the delivery side of pump 10 and,by a second conduit 15, to reservoir 11.. A third conduit 16 connectsthe distributor to the first chamber 4, while a fourth conduit 17connects this distributor to the second chamber 5.

Furthermore, a non-retum valve 18 is arranged in the fourth conduit 17,so as to allow passage of the fluid from the distributor 13 towards the:second chamber 5. It will also be noted that an adjustable flow-limiter19, which is more particularly described with reference to FIG. 2, isarranged in a fifth conduit 20, which is connected to the fourth conduit17 on either side of nonretum valve 18. A sixth conduit 21, which isconnected to the third conduit 16, is also connected to the organ foradjusting the opening of flow-limiter 19, as will be observed below withreference to FIG. 2.

Finally the communications established by distributor 13 will be noted,which distributor connects:

in its first position, on the one hand, the first conduit 14 and thethird conduit 16, and on the other hand, the second conduit 15 and thefourth conduit 17;

in its second position, on the one hand, the first conduit 14 and thefourth conduit 17 and, on the other hand, the second conduit 15 and thethird conduit 16;

and which, in a third position, which is intermediate between the firstand second positions, on the one hand, connects the first conduit 14 andthe second conduit 15 and, on the other hand, isolates the third conduit16 and the fourth conduit 17 at its position.

It will be understood that the hydraulic driven part supply circuitgiven as an example does not limit the application of the invention tothis single embodiment. A particular alternative would be application tothe case in which the pump has regulation of its flow, and this wouldthen be a closed-circuit supply, which is conventional in hydraulics anddoes not require a reversing distributor.

The flow-limiter 19 shown in FIG. 2, comprises the two following,distinct elements:

a discharge-valve 22, which is guided by vanes 23,

which are arranged in a bore 24 formed in the body 25 of flow-limiter19, and which can be in contact with its seat 26 under the influence ofan adjusted spring 27;

a valve with adjustable opening, consisting of a slide 28, which isslidably mounted in body 25, and which has a shoulder 29, which isprovided with grooves 30 of variable sections and the lateral wall 34ofwhich overlaps the edge 31 of a throat 32 formed in body 25. A weaklyadjusted spring 33 tends to return slide 28 in the direction of closureof conduit 20 by lateral wall 34, and does so by acting on an endsurface 29a of slide 28.

In addition, slide 28 has a second end surface 29b and an intermediatesurface 29c, which is directed in the opposite direction to surface 29b.It will be noted that conduit 20 is in fact divided into three sections,which are connected, one to second chamber 5 of ram 1 and to an intakeconduit 35 of body 25, and another to distributor l3 and to an outputconduit 36 of body 25 and, finally, an intermediate section, also knownas the internal conduit, which connects throat 32 to dischargevalve 22.The pressure of the fluid contained in the said intermediate section ofconduit 20 acts on surface 290, in the same direction as spring 33, andhas an influence antagonistic to that of the pressure of the fluidcontained in conduit 21, which acts on end surface 29b of slide 28.

FIG. 3 shows an advantageous modification of flowlimit'er 19, in which acomplementary piston 37 is slidably mounted in body 25 at throat 32. Aspring 38 is connected between piston 37 and body 25, and tends to keepsurface 39 of the said piston 37 in contact with end surface 29a ofslide 28.

A first channel 40 is formed in piston 37, through which it passes. Itconnects a first volume 41, which is defined by throat 32 and opens intothe portion of conduit 20 connected to the discharge-valve, to a secondvolume 42, which is closed and is in fact, in this particular case,closed by a plug 43. A nonreturn valve 37a, consisting of aball-bearing, its plunger and a return spring only allows passage offluid in channel 40 from the first volume 41 towards the second volume42. Moreover, the ball bearing and its plunger are guided by vanes 44rigidly connected to piston 37. Furthermore, another, calibrated channel45 connects the two volumes 4] and 42, in this particular case via aportion of first channel 40, and forms a restriction for the pas sage ofthe fluid.

The operation of the supply apparatus described above is explainedbelow.

Distributor 13 is firstly arranged in its second position. The fluiddrawn by pump 10 from reservoir 11 through suction conduit 12 isdelivered into first and fourth conduits 14 and 17. This fluid passesthrough non-return valve 18 and enters chamber 5 of ram 1. The effect ofthe pressure of the fluid in chamber 5 on piston 2 is to push thispiston and, therefore, to lift load 7, which is linked to piston rod 6.Meanwhile, the fluid contained in chamber 4 is delivered into reservoir11, through third conduit 16, distributor 13 and second conduit 15.

When load 7 has been lifted, distributor 13 is arranged in its thirdposition. This results in the closure of third and fourth conduits 16and 17, and thus in shutting the fluid contained in chambers 4 and 5 inclosed volumes. Load 7 is, therefore, immobilised, while pump 10 returnsto reservoir 11 through first conduit 14, distributor 13 and secondconduit 15.

The two operating phases just described were in fact already knownthemselves prior to the present invention and have only been recalled asa reminder.

On the other hand the operating phase which will now be described isnovel and, of course, relates to the specific means in accordance withthe invention. This operating phase corresponds to the distributor beingplaced in its first position.

It will firstly be stated that the fluid delivered by pump 10 enterschamber 4 via first conduit 14, distributor 13 and third conduit 16.Moreover, the fluid contained in chamber 5 cannot escape through thewhole of conduit 17, as it is prevented from doing so by nonreturn valve18. This fluid can therefore only escape from chamber 5 through conduit20, and this through flow-limiter 19, in the manner which will beexplained below.

However, before examining the operation of the actual flow-limiter 19,it will briefly be mentioned that the necessity for the insertion ofthis limiter is linked with the fact that load 7 is such that it tendsto drive the pis ton in the same direction as the fluid which enterschamber 4 tends to do itself, but more rapidly than the said fluid cando so. In other words, in the absence of a flow-limiter, such as limiter19, the flow of fluid conveyed by conduit 16 would be insufficient tocompensate for the increase in volume of chamber 4, due to the drivingof piston 2 and the piston-rod by load 7. There would therefore be arisk of cavitation in chamber 4, cavitation always being detrimental tothe maintenance of the wholeness of the organs which give rise to it andto the maintenance of satisfactory operating conditions. The reason forthe presence of flow-limiter 19 is to avoid such disadvantages.

It will also be noted that, if the example selected is one in which thereversible drive organ linked to load 7 consists of ram 1, allreversible drive organs can be supplied by means of the apparatus whichhas been described. Thus, in particular, a reversible hydraulic motorattached to a winch drum, could be driven by the load suspended from theconnecting line wound on the said drum. The apparatus which has beendescribed in the example of the supply of ram 1 could, of course, find awell-advised application in the supply of the said motor for driving thewinch.

The operation of flow-limiter 19 will now be explained. The fluiddelivered from chamber 5 arrives opposite shoulder 29 of slide 28. Theposition of this slide has been governed by the equilibrium of theantagonistic influences, on the one hand, of the pressure of the fluidcontained in third conduit 16, which, by acting through sixth conduit 21on surface 29b, tends to cause opening of a passage between edge 31 andthe lateral wall 34 and grooves 30 of shoulder 29 and, on the otherhand, of the pressure of the fluid contained in the portion of conduit20 between throat 32 and dischargevalve 22, and of spring 33.Furthermore, spring 33 has a very small and negligeable influencerelative to that of the pressure of the fluid in the said portion ofconduit 20, which pressure corresponds to the adjustment of spring 27 ofdischarge-valve 22. The purpose of spring 33 is in fact limited toreturning slide 28 to the position corresponding to closure of theabovementioned passage between edge 31 and shoulder 29, when thepressure in the various conduits becomes substantially zero followingprolonged stoppage of operation.

A given passage is therefore formed between the two portions of conduit20 which can be isolated by shoulder 29. The size of this passage isdirectly governed by the pressure in sixth conduit 21. Now this pressureis either low, when load 7, driving piston 2, tends to form a vacuum inchamber 4 and consequently in third conduit 16 and sixth conduit 21, orhigh, when, on the other hand, load 7 does not drive piston 2 morerapidly than compensation is effected for the volume increase in chamber4 by addition of fluid delivered by pump 10.

When the pressure of the fluid in the sixth conduit 21 is initially low,there is a reduction in the said passage, under the influence of thepressure of the fluid contained in the portion of conduit 20 arrangedbetween throat 32 and discharge-valve 22, which pressure is maintainedsubstantially constant by the said discharge-valve 22, which isadjusted. This passage reduction causes a reduction in the flow of fluidconveyed in conduit 20, and therefore deceleration of the motion of thepiston 2. The increase in the volume of chamber 4 therefore alsodecreases until the fluid delivered by pump 10 can compensate for thisvolume increase. Only then, the pressure in third conduit 16 and,consequently, in sixth conduit 21 again adopts a higher value until the,pressure drop in chamber 4, which results from this rapidity of descentof piston 2, causes a drop inthe pressure of the fluid contained insixth conduit 21 and, in this way, causes the return of slide 28 to itsmedian position in which the flow-rate in conduit 20 corresponds to therequired value of the descent velocity of piston 2 and load 7.

Flow-limiter 19 acts in two distinct phases: a phase in which thepressure of the fluid contained in chamber 5 is reduced, by possiblethrottling of the fluid between edge 31 and the lateral wall 34 andgrooves 30 of shoulder 29, during which phase there is a consumption ofpower due to throttling, which is equal to the product of the flow-rateand the pressure differential between the fluid contained in chamber 20on either side of shoulder 29;

a phase in which the pressure of the fluid contained in the portion ofconduit 20 between throat 32 and adjusted discharge-valve 22 isstabilized, which stabilization corresponds to the value of theadjustment of spring 27 of the said discharge-valve 22.

This arrangement has considerable advantages. In

fact it will be clearly understood that better operational stabilizationis obtained than by the use of the previtially constant, which is notthe case of the return force of a spring.

Furthermore, it is very easy to adjust the opening time of theabovementioned passage, as a function of the values of the usefulsections of surfaces 29b and 290.

Finally, the operating pressiire of the fluid contained in sixth conduit21 is in fact maintained at a substantially constant value which,moreover, is lower than in prior apparatus. These two points arenaturally advantageous in themselves.

To perfect the stabilization obtained from the operation of flow-limiter19 of FIG. 2, it is possible to advantageously add a shock-absorber forthe motion of slide 28 corresponding to the opening of theabovementioned passage, such as the shock-absorber described withreference to FIG. 3.

Supposing that slide 28 has initially been entirely pushed until secondvolume 42 has become minimal, an examination will firstly be made of thefollowing phase, in which slide 28 slides in the direction opposite tothe initial direction, and then of the phase after this following phase,in which slide 28 again slides in the direction of reduction of secondvolume 42.

While slide 28 moves in the direction opposite to the initialdisplacement direction, piston 37 moves under the influence of spring 38in the same direction as the slide. The pressure of the fluid containedin first volume 41 has the effect of pushing back the ball-bearing andthe plunger of non-return valve 37a and thus allow ing free transfer ofthe fluid from the first volume 41 into the second volume 42, viachannel 40.

When the closure movement of slide 28 has been terminated, anotheropening movement takes place. However, this opening movement is brakedby the fluid which, enclosed in second volume 42, can only now escapefrom it through calibrated channel 45, channel 40 then being re-closedby non-return valve 37a. It will therefore be understood that piston 37,non-return valve 37a and calibrated channel 45 in fact form a trueshock-absorber for the motion of slide 28 corresponding to the openingof the passage. This shock'absorber naturally perfects stabilization ofthe motion of slide 28 and also, therefore, the operation of theassembly.

Of course, it will be noted that an equivalent would be to formnon-return valve 37a and calibrated channel 45 in body 25 of theflow-limiter, seeing that the functions provided remain identical.

Also, if the example described corresponds to the open-circuit supply ofa ram 1 by means of a distributor 13, the present invention is alsoapplicable to the case of closed-circuit" supply by means of areversible pump with flow-rate regulation. In a conventional manner,such a pump is connected to the supply circuit by two main conduitswhich, depending on the position of the flow-regulating organ,constitute either one suction conduit and the other the deliveryconduit, or, conversely, one the delivery conduit and the other thesuction conduit. The portion of the circuit connected to the suctionconduit, by analogy with the case of the open circuit, then constitutesthe fluid reservoir. It is worth noting that, in the case of theclosed-circuit, the organ for regulating the flow-rate of the pumpselects the delivery direction of the said pump and, in that respect,can be considered as equivalent to the distributor 13 of theopen-circuit.

The invention is not limited to the description given above but, on thecontrary, covers all the modifications which could be made to it,without departing from its scope or spirit.

l claim:

1. Apparatus for supplying fluid to a reversible drive organ, which islinked to a load which provides its forced drive during the operatingphase in question and which has first and second chambers, this supplyapparatus consisting of:

a fluid reservoir,

a pump connected to the said reservoir by a suction conduit,

a first conduit which connects the delivery side of the pump to thefirst of the said chambers, this first chamber forming the fluid intakechamber during the above-mentioned operating phase,

a second conduit which connects the second of the said chambers to thereservoir, this second chamber forming the fluid delivery chamber duringthe said operating phase,

a non-return valve which is arranged in the second conduit and onlyallows passage of the fluid towards the latter chamber,

a third conduit which is connected to the said second conduit on eitherside of the non-retum valve and in which an adjustable flow-limiter isarranged,

a fourth conduit which is connected, on the one hand, to the firstconduit and, on the other hand, to the flow-regulating organ of the saidflowlirniter, characterised in that the adjustable flowlimiter itselfconsists of:

an adjusted discharge-valve, which acts to maintain the pressure of thefluid which can be contained in the portion of the third conduit whichis connected to the said discharge-valve and is arranged directlydownstream of this valve relative to the reservoir, substantially equalto a given value,

and a valve with adjustable opening, which is arranged between the driveorgan and the dischargevalve and is distinct from this discharge-valve,and the function of which is to regulate the value of the pressure ofthe fluid which can be delivered out of the second chamber during theabove-mentioned operating phase, while this valve with adjustableopening has an organ for adjusting its opening, which is in equilibriumunder the antagonistic influences, on the one hand, of the pressure ofthe fluid contained in the fourth conduit and, on the other hand, of thefluid pressure which is substantially equal to the given value.

2. Supply apparatus in accordance with claim 1, characterised in that inaddition the valve with adjustable opening is provided with ashock-absorber for its opening motion, in that the said shock-absorberconsists of a piston, which is linked to the organ for adjusting theopening of the said valve with adjustable opening, being mountedslidably in the body of the said valve, and which defines with the saidbody, on the one hand, a first volume, which is freely in communicationwith the portion of the third conduit connected to the discharge-valve,and, on the other hand, a second volume, in that the non-retum valveallows passage of the fluid from the first volume towards the secondvolume, while a calibrated channel, forming a restriction, connects thesaid two volumes, and in that a retaining organ tends to keep the saidpiston and the said adjustment organ linked together.

3. Supply apparatus in accordance with claim 1, characterised in thatthe organ for adjusting the opening of the valve with adjustable openingconsists of a slide mounted slidably in the body of the said valve, inthat the said slide has a shoulder, the adjacent lateral wall of whichcan overlap the edge of a throat formed in the said valve-body, and inthat one of the elements, lateral wall of the shoulder or edge of thethroat, is provided with grooves of progressively variable sections.

4. Supply apparatus in accordance with claim 1, characterised in that inaddition an elastic return organ is inserted between the organ foradjusting the opening of the valve with adjustable opening and the bodyof the said valve and has an influence antagonistic to that of thepressure of the fluid contained in the fourth conduit.

1. Apparatus for supplying fluid to a reversible drive organ, which islinked to a load which provides its forced drive during the operatingphase in question and which has first and second chambers, this supplyapparatus consisting of: a fluid reservoir, a pump connected to the saidreservoir by a suction conduit, a first conduit which connects thedelivery side of the pump to the first of the said chambers, this firstchamber forming the fluid intake chamber during the above-mentionedoperating phase, a second conduit which connects the second of the saidchambers to the reservoir, this second chamber forming the fluiddelivery chamber during the said operating phase, a non-return valvewhich is arranged in the second conduit and only allows passage of thefluid towards the latter chamber, a third conduit which is connected tothE said second conduit on either side of the non-return valve and inwhich an adjustable flow-limiter is arranged, a fourth conduit which isconnected, on the one hand, to the first conduit and, on the other hand,to the flow-regulating organ of the said flow-limiter, characterised inthat the adjustable flow-limiter itself consists of: an adjusteddischarge-valve, which acts to maintain the pressure of the fluid whichcan be contained in the portion of the third conduit which is connectedto the said discharge-valve and is arranged directly downstream of thisvalve relative to the reservoir, substantially equal to a given value,and a valve with adjustable opening, which is arranged between the driveorgan and the discharge-valve and is distinct from this discharge-valve,and the function of which is to regulate the value of the pressure ofthe fluid which can be delivered out of the second chamber during theabove-mentioned operating phase, while this valve with adjustableopening has an organ for adjusting its opening, which is in equilibriumunder the antagonistic influences, on the one hand, of the pressure ofthe fluid contained in the fourth conduit and, on the other hand, of thefluid pressure which is substantially equal to the given value. 2.Supply apparatus in accordance with claim 1, characterised in that inaddition the valve with adjustable opening is provided with ashock-absorber for its opening motion, in that the said shock-absorberconsists of a piston, which is linked to the organ for adjusting theopening of the said valve with adjustable opening, being mountedslidably in the body of the said valve, and which defines with the saidbody, on the one hand, a first volume, which is freely in communicationwith the portion of the third conduit connected to the discharge-valve,and, on the other hand, a second volume, in that the non-return valveallows passage of the fluid from the first volume towards the secondvolume, while a calibrated channel, forming a restriction, connects thesaid two volumes, and in that a retaining organ tends to keep the saidpiston and the said adjustment organ linked together.
 3. Supplyapparatus in accordance with claim 1, characterised in that the organfor adjusting the opening of the valve with adjustable opening consistsof a slide mounted slidably in the body of the said valve, in that thesaid slide has a shoulder, the adjacent lateral wall of which canoverlap the edge of a throat formed in the said valve-body, and in thatone of the elements, lateral wall of the shoulder or edge of the throat,is provided with grooves of progressively variable sections.
 4. Supplyapparatus in accordance with claim 1, characterised in that in additionan elastic return organ is inserted between the organ for adjusting theopening of the valve with adjustable opening and the body of the saidvalve and has an influence antagonistic to that of the pressure of thefluid contained in the fourth conduit.